The present invention is directed generally to a method and system for controlling brake-application energy in a vehicle combination including a tractor vehicle equipped with an electronic braking system (EBS) and a trailer vehicle.
It is known that vehicle combinations (comprising a tractor vehicle having front and rear axles as well as a trailer vehicle) can be provided, on the one hand, with a vehicle deceleration control function, otherwise known as “Z-control,” and, on the other hand, with coupling force control between the tractor vehicle and the trailer vehicle.
EP 0 697 314 B1 describes, for load-dependent control of brake pressure in a vehicle combination, a method designed to brake the trailer and tractor vehicles as equally as possible by appropriate distribution of brake pressure to the axles of the tractor vehicle and trailer vehicle. For this purpose, an initial value of a reference factor is determined by means of a set of performance characteristics resident in the tractor vehicle electronics and of the measured instantaneous tractor vehicle condition. The initial value is located in a band within the normal range; the reference factor is defined as the ratio of total brake pressure of the tractor vehicle to set vehicle deceleration (this ratio being a function of tractor vehicle condition data containing at least one description of load condition); and the set of performance characteristics containing a band of reference factor values within the normal range. The total brake pressure of the tractor vehicle is adjusted to a value specified by the initial value of the reference factor, and the brake pressure of the trailer vehicle is adjusted to a value, within a predetermined resident braking band, that corresponds to the selected set vehicle deceleration of the trailer vehicle.
According to EP 0 697 314 B1, during braking, the actual vehicle deceleration is measured and, if a deviation from the set vehicle deceleration is detected, the total brake pressure of the tractor vehicle is first corrected by readjusting the value of the reference factor in the band within the normal range. If the value of the reference factor reaches a limit point for the band within the normal range during such readjustment, the brake pressure for the trailer vehicle is readjusted in the predetermined braking band. Readjustment of the brake pressure for the trailer vehicle continues until the reference factor for the tractor vehicle total brake pressure corresponding to the altered trailer vehicle brake pressure is once again located in the band within the normal range.
The coupling force control function described in EP 0 697 314 B1 is not provided with any limits differing from those of the vehicle deceleration control function. As long as the vehicle deceleration control function is located within its working range, the coupling force control function is also active. The total braking performance is adjusted only via the trailer vehicle, with the disadvantage that any temperature difference that may exist between the wheel brakes of the trailer vehicle and tractor vehicle becomes even greater due to this control.
Another disadvantage of the method described in EP 0 697 314 B1 is that vehicle deceleration control does not take place in a manner adapted to individual axles. Also, adjustment or adaptation to the braking behavior of the vehicle combination is slow, and the braking process is subject to numerous control interventions due to the simultaneous vehicle deceleration control (Z-control) and coupling force control, reducing braking comfort. Additionally, there are longer dead times and thus larger deviations between actual and set performance.
EP 0 885 793 A2 of WABCO GmbH describes, for braking a vehicle, a method in which the load condition of the vehicle is determined by a load signal, which is formed from a logic signal, which is used as a logic signal linking the vehicle driver's intent and the associated braking force.
EP 0 445 575 B1 describes, for distribution of brake pressure to the axles of a vehicle having anti-lock brake system (ABS) pressurized fluid brakes, a method in which adaptive adjustment of the brake pressure distribution to the axles of the vehicle, or in other words the ratio between front axle and rear axle brake pressure, takes place on the basis of a model in which this ratio, starting from a static pressure ratio, changes linearly with the set vehicle deceleration. The static pressure ratio depends on the load condition and is not influenced by the braking forces of a trailer vehicle. The current value of brake pressure distribution at a given time is used as the basis for the subsequent braking processes until the monitored inter-axle speed difference exceeds a predetermined limit value, after which a new brake pressure distribution function is determined as a function thereof.
EP 0 357 983 B1 describes, for load-dependent control of the brake pressure of a commercial vehicle, a method whereby, in a range below the active capability of ABS, the brake pressure ratio and a reference factor are readjusted from their starting values if the wheel speed differences, for example the deceleration control difference between the axles of the vehicle, exceed predetermined limit values. The brake pressure ratio is the ratio between front axle and rear axle brake pressures of the vehicle; the reference factor determines the total braking level and is defined as the ratio of total brake pressure to set vehicle deceleration. Readjustment of the brake pressure ratio and the reference factor takes place in a self-learning procedure.
It is desired to provide a method and system whereby automatic load-dependent braking force control (load sensing function) can be applied for the trailer vehicle, so that control improvements over conventional methods for controlling brake-application energy in vehicle combinations without a trailer vehicle load sensing function can be realized. Such advantages include, in particular, rapid adaptation of the control system to the respective driving and load conditions with short dead times and high braking comfort.